1. Field of the Invention
Embodiments of the present invention generally relate to a support ring to support a substrate in a process chamber.
2. Description of the Related Art
In the processing of substrates, such as semiconducting substrates, the substrate is placed on a support in a process chamber and suitable processing conditions are maintained in the process chamber. For example, the substrate can be heated in a controlled heating cycle to thermally process the substrate. The substrate can be heated, for example, by an array of heating lamps disposed above and/or below the substrate in the chamber. Thermal processing can be used, for example, to anneal a layer that has been ion-implanted on the substrate, perform thermal oxidation or nitridation processes, or perform thermal chemical vapor deposition processes on the substrate.
It has been observed that variations in temperature gradients across the substrate can result in non-uniform processing of the substrate. Non-uniform temperatures occur at different substrate regions because of non-uniform convection or conduction heat losses from regions of the substrate in contact with the support (or other chamber components) and substrate regions not in contact with the support. The temperature gradients in the substrate have been reduced using a substrate support ring that extends inwardly from the chamber wall and surround a periphery of the substrate. Particularly, the substrate to be thermally processed is supported on its periphery by an edge of the support ring having an annular lip contacting the edge of the substrate. The support ring effectively expands or pushes out the temperature gradients in the substrate from the substrate periphery to the outer edges of the support ring. The overlapping of the substrate and the support ring also prevents or minimizes the leakage of the high-temperature radiant energy from the radiant heat source (disposed above the substrate) around the edge of the support ring on either its inner or outer side.
Support rings having an annular edge can fail to provide adequate temperature uniformity across the substrate in rapid heating rate processes, for example, processes having heating rates of at least about 200° C./second. In these processes, the difference in heating rates between the support ring and the substrate generates temperature gradients along the periphery of the substrate that become unacceptably high during the heating process step. The substrate may also experience azimuthal temperature variations caused by azimuthal variations in solid-solid thermal contact, largely by virtue of variable surface finish and planarity/flatness between the substrate and the support ring. In certain situations, since the substrate and the annular lip of the support ring overlap near the edge of the substrate, it is difficult to achieve uniform temperature profile near the edge by measuring and adjusting the temperature of the substrate alone. Depending on the support ring's thermal properties relative to the substrate's thermal and optical properties, the temperature profile of a substrate is generally either edge high or edge low. It is particularly difficult to achieve temperature uniformity across the substrate especially when the substrate is heated at rapid heating rates, such as in rapid thermal processing (RTP) systems.
Accordingly, it is desirable to have an improved support ring that prevents or minimizes any azimuthal variations in the overlap region between the substrate and the support ring so that the support ring does not generate excessive temperature gradients in a substrate during thermal processing.